Not all airports have control towers, but it is essential
that the pilot become familiar with the requirements and procedures where
a control tower is used. Today's airport congestion resulted in the "airport
traffic area" concept of traffic control for those airports that have a
control tower in operation. Where an airport traffic area exists, it extends
to a radius of 5 statute miles from the center of the airport, and extends
up to (but not including) 3,000 feet above the airport surface (Fig. 7-5).
Airport traffic areas are not depicted on aeronautical charts, but the
airports at which these areas exist are identifiable on the charts by a
control tower radio frequency and the letter CT adjacent to the airport
symbol. Complete radio data for each airport having radio communication
facilities is found in the Airport/Facility Directory

When operating at an airport where traffic control is being
exercised by a federally operated control tower, pilots are required to
maintain two way radio communication with the tower while within the airport
traffic area, unless the tower authorizes otherwise. Through this communication
the pilot requests permission from the tower operator to taxi, take off,
or land and receives a specific clearance along with pertinent information
about the traffic pattern.

The tower controller will issue clearances (instructions)
for aircraft to generally follow the desired flightpath (traffic pattern),
as well as the proper taxi routes when operating on the ground. If not
otherwise authorized or directed by the tower, pilots approaching to land
must circle the airport to the left. However, an appropriate clearance
must be received from the tower before the landing may be made.

Airport traffic control is based upon observed, or reported known traffic,
and airport conditions. Tower controllers establish the sequence of arriving
and departing aircraft by requiring pilots to adjust their flightpaths
and speeds as necessary to achieve proper spacing. These adjustments can
only be based on observed air traffic, accurate position reports from pilots,
and anticipated aircraft maneuvers.

On occasion it may be necessary for a pilot to maneuver the aircraft
to maintain spacing with other traffic. The controller can anticipate minor
maneuvering such as shallow "S" turns. The controller cannot, however,
anticipate a major maneuver such as a 360 degree turn. If a pilot makes
a 360 degree turn after obtaining a landing sequence, the result is usually
a gap in the landing interval and more importantly, it causes a chain reaction
which may result in a conflict with following air traffic, and interruption
of the sequence established by the tower or approach controller. Should
a pilot decide to make maneuvering turns to maintain spacing behind a preceding
aircraft, it is necessary to advise the controller. Except when requested
by the controller or in emergency situations, or when receiving radar service,
a 360 degree turn should never be executed in the traffic pattern without
first advising the controller.

Procedures in which light gun signals are used apply only
when the aircraft using the particular airport is not equipped with two
way radio, or when radio contact cannot be established or maintained (Figs.
7-6 and 7-7).

In addition to directing all incoming and outgoing air
traffic by radiotelephone or light gun signals, the tower also provides
current weather data, altimeter setting, and any other information necessary
to safe flight within the airport traffic area.

Tower operators are all licensed by the FAA, and the towers
themselves are in most cases under the jurisdiction of the FAA, although
some are independently run by the individual airport operator. If the tower
is not Federally operated, communications are required if the aircraft
is equipped with radio. If the aircraft's radio allows only reception from
the tower, a listening watch should be maintained.